Night vision apparatus is a term which is used herein to mean apparatus useful for observations under conditions where there is insufficient visible light for normal visual observation and which may thus be useful in caves and other dark places as well as at night. For many years, such apparatus has been used by the military because they provide enormous tactical advantages over forces which lack them. Military night vision apparatus is typically “passive” in the sense that it relies upon infrared radiation naturally present in the environment and/or low levels of light emitted by objects being observed. Infrared night vision apparatus visualize heat given off by observed targets while passive night vision apparatus gathers low levels of available radiation and images it on to a image intensifier tube, which amplifies the low level radiation several thousand fold and presents a visible representation of the resultant amplified image to the user. Infrared passive apparatus is desirable for military use because it gives an indication of the temperature of the object being viewed, warmer objects appearing brighter than colder ones. Thus, a passive night vision apparatus can be used, for example, to reveal vehicles (and especially the hot exhaust systems thereof) against a cold ground, or warm-blooded animals against a similar cold background. Also, it is obviously undesirable for a military night vision apparatus to require emission of radiation, since any enemy equipped with a night vision system could readily detect the emissions and thus uncover the location of forces using them.
Many people have been intrigued by newscasts and other public displays of images generated by military night vision apparatus and wish to experiment with similar apparatus either simply as a novel experience or, for example, because such apparatus may be useful in observing wild life at night or under other low light conditions such as in caves without the need to generate visible light which might drive off the wild life. However, the infrared imaging detectors and image intensifier tubes used in military systems are very expensive; even in mass production, the standard night vision image intensifier apparatus used by U.S. infantry forces costs about $3500 per unit, which is prohibitive for most civilian applications. Furthermore, because military apparatus designed to detect radiation emitted from objects not greatly above ambient temperature (at say 40° C.), the apparatus is designed to be sensitive to far infrared radiation having wavelengths above about 2000 nm. Images generated using such far infrared radiation are so different from images of the same scene in visible light that specialized training is typically needed to enable military personnel to perform tasks such as driving vehicles while using night vision apparatus.
Accordingly, there is a need for an inexpensive night vision apparatus which can be used safely by the general public without the need for specialized training. Desirably, such apparatus should be compact, have sufficiently low power requirements that it can be operated from batteries, and produce images based upon visual properties of the environment such that the images are easy for even inexperienced operators to interpret. It is a primary object of this invention to fulfil this need.
It is a further object of this invention to provide such apparatus which does not emit substantial amounts of visible radiation.
It is yet another object of this invention to provide such apparatus in head-worn and hand-held versions.
Other objects of the invention will be apparent and will appear hereinafter in the following detailed description when read in connection with the drawings.